Plating products (for example, decorative plating products for automobiles such as emblem) of which a substrate is comprised of ABS resin (high polymer materials) have been proposed. The important property in the plating products of this type is adhesiveness of the metal film (plating film) formed on the substrate by a plating technique. When the adhesive strength is weak, the metal film is easily peeled off. It signifies an increase in reliability of the products that the adhesiveness of the metal film is large.
So as to improve the aforementioned adhesiveness, it has been proposed to form fine irregularities on the substrate surface. That is, it has been proposed to make the surface of the substrate rough. With this, what is called an anchor effect is expected, and the adhesion is improved.
The etching technique using oxidizing agents (for example, aqueous solutions of permanganate, hexavalent chromic acid, and the like) is well known as a technique of making the surface of the substrate rough. However, it is only in the case of resin having an unsaturated group like an ABS copolymer that the etching technology using the hexavalent chromic acid can be employed. For this reason, a constraint is putted on the substrate materials. In addition, in recent years, the use of the hexavalent chromic acid has been strongly regulated. This promotes a search for materials that replace the hexavalent chromic acid. However, in the current situation, no effective measure exists yet.
High integration and densification are required for the circuit substrates as the technology progresses. From this viewpoint, it is preferred that the fewer the irregularities existing on the copper foil surface of the substrate, the better. However, there are the irregularities on the metal film (for example, copper film) formed on the etched substrate surface. When the metal film (copper film) has the irregularities, a propagation distance of signals that flow on the metal film is made long. A propagation loss (attenuation of signals) is also made large. In addition, heat generation occurs. Thus, it is preferred that an irregularity degree of the metal film (copper film) is few. That is, the substrate having a small surface roughness is desired.
A semi-additive technique has started to be employed for establishing wiring circuits in the circuit substrates to cope with a resource problem of copper and a progress in refinement of wiring patterns. The substrate having a small surface roughness is desired from such a viewpoint as well.
A corona discharge treatment (or plasma discharge treatment) is known as a technique of enhancing the adhesiveness between the substrate and the metal film. With the treatment of this type, the OH groups are introduced into the substrate surface. It is said that existence of this OH group contributes to enhancing the adhesiveness of the plating film formed thereon.
However, there exists an anxiety that the corona discharge treatment (or plasma discharge treatment) might deteriorate the substrate. And yet, even though the OH groups are generated, the number thereof is not much. From this, there was a restriction to improvement of the adhesiveness. In addition, the corona discharge treatment (or plasma discharge treatment) puts a constraint to shape or size of to-be-treated substances. Moreover, workability of the discharge treatment is also not good.